Telephone exchange system



Jan. I 12, 1932.

H, HOVLAND TELEPHONE EXCHANGE SYSTEM Filed March 24, 1930 BUS Y 3 Sheets-Shea I H 5&

INVENTO/P HHal LA/vo A TTO/FNE Y Jan. 12, 1932. H' V ND 1,841,123

TELEPHONE EXCHANGE SYSTEM Filed March 24, 1930 3 Sheets-Sheet 3 lNVENTOf? HHOVLAND B Y A TTORNE Y Patented Jan. 12, 1932 UNITED STATES PATENT OFFICE A HENRY HOVLAND, OF WILLISTON PARK, NEW YORK, ASSIGNOR TO BELL TELEPHONE LABORATORIES, INCORPORATED, OF NEW YORK, N. Y., A. CORPORATION OF NEW YORK TELEPHONE EXCHANGE SYSTEM Application filed March 24, 1930. Serial No. 438,863.

I change is equipped with a selecting unit comprising a plurality of separately operable switches one of which serves to extend a local calling line over an interotfice trunk to the i main exchange, another to extend the calling line to local switches so the call may be completed to a local called line when it has progressed far enough to determine that this is its destination, and another to extend the callis ing lineto special service trunks suchas those leading to operators positions.

' Another feature, is a system. in which the interotfice trunk seized by the selecting switch is provided with a repeater for repeating impulses to set switches at the main ofiice, said repeater being equipped with aregister for recording the oflice code digits sent by thecalling subscriber and repeated tothe main office; As soon as all code digits have been .1;- reccrded, the register exercises control over said selecting unit to determine whether the call is to continue its progress in the main ofiice and'the temporarily seized local trunk released, whether the interoffice trunk is to be released and the calling line extended locally to the called line, or whether both the interoifice trunk and the seized local trunk are to be released and the calling line extended over one of the special service trunks.

4,2: Another feature of the invention is a system in which two groups of trunks appear in the same row of contacts in a switch bank,

each trunk being provided withan individual I,

relay, the relays of one group serving when released to maintain an artificially busy conditionon the respective trunks and the relays of the other groups serving the same purpose when energized, and in which selective means is provided for selectively energizmg e the relays of either group.

brushes of selector switch S In the drawings, Fig. 1 illustrates a subscribers line terminating in the bank of a line finder switch in a branch ofiice and also a portion of a trunk circuit extending from the brushes of the finder switch.

Fig. 2 discloses three separate selector switches each terminating a branch of said trunk circuit, one of said switches serving to extend the trunk in the direction of the central oflice, another to extend the trunk to local selector switches, and the third one to extend the trunk to operators positions. Fig. 2 also illustrates diagrammatically the local selectors anda local called line andthe operators trunks. I

Fig. 3 shows a repeater circuit located at the branch oflice in the outgoing end of the trunk circuit which extends to the distant central ofiice and there terminates in selector switches for completing a connection to a called line. I

A calling subscribers line in the branch office is extended by means of a finder switch F to a trunk having three different branches or outlets. ing the talking conductors 125 and 126, extends to the brushes of the selector switch S-1, which has access to trunks such as the trunk 127 leading to the outgoing repeater R. The second branch, comprising the talking conductors 128 and 129, extends tothe 2, which has access to local trunks such as the trunk 130 leading to local first selectors such as the switch 8-4. The third branch comprises the talking conductors 131 and 132 and extends to the brushes of selector switch S 3, which has access to two different kinds of trunks, some extending to special service operators positions and others extending to toll recording operators positions. The special service trunks and the toll recording trunks may appear in any desired relation in the bank of the switch S3. As illustrated, for example, the brushes of the switch 8-3 in theirjfirst position make connection with the special service trunk 222; in their second position, they connect with the recording trunk 223; in their third position,

theyconnect with another special service- One of these branches, compris-- subscriber dials the first code digit, the im-- trunk 22; and in their fourth position they connect with a recording trunk 225.

A calling line in the branch oliice is first extended to the brushes of the selector S-1, and this selector is set in operation to seize an idle repeater andtrunk outgoing to the central oilice. Since it is desirable'to have a uniform number of digital places inthedesignation of acalled line whether the call isbeing extended-to a local subscriberinthe branch otfice or to a central oiiice subscriber, and since it is necessary to distinguish between local and central oflice calls, the system herein disclosed is arranged'to utilize the-first portion of the entire designation asa code 'toenable the apparatus to distinguish between-the local and centraloiiice calls. The codem-ay consist of either one or two digital places. he illustratet in the drawings, it is assumed that the code comprises the first two digital places in-the designation. Whenthe pulses are repeatedby the repeater R- over 'the trunk'32l to operate the selector switch fS'-.6. These impulses also operatet-he stepby-step register switch associated with the repeater R. The register switch transfers its registration'to other parts of the appara- "tusfand at the end of the-firstseriesofimpulses, it automatically releases. The first operation of theregister switch initiates the operation of-th'e switch S -2, which searches and'fin'ds the first'idle trunk 130 extending to the'localj selector switch 'S4.' In this manner a.connection to an idle local-selector is prepared in advance in anticipation of a local call. 'The' impulses representing'thesecond code digit are likewise repeatedto the central office to set thesucceedingselector switch S7 a'nd'also to'cause the second positioning of the register switch; The two settings of the register switch are suiiicient to. deter- *mine the "destination of the call, namely, whether it isto continue'its progress through the "central office, whether it'is =tobe routed to switches in the local Office, or whether it should be extended over a'trun'k to an operators position. If the call is to continue its progress in the central office, succeeding impulses are repeated over the trunk 321 'caus ingthe settingof the remaining switches and V ;the completion of the connection'to a called subscribers' line-320. If, however, the calljis a local one, the-repeater R andtrunk 321 are released, the calling subscribersline discon: nected from the switch S-1,.and extendedover the switch'S2-.to the preselected trunk.

'130extending to a first local selector switchv Si-4. COIltlnHlIlg series of impulses cause {the set-ting of the local-switchesto' complete the connection to the local called line 221. v Shouldthe calling-subscriberwish to make a special-service call to an operator s position,

:he dials: aspecial-code consisting ofthe single digit 0. This results 'in the release of the line.

.cuit-offthe magnet 200 and extending central oflice trunk and the operation of the selector switch S-3, which automatically tests the trunks in its bank and seizes the first idle one leading to the special operators position. On the other hand, should the calling subscriber wish toobtain a toll re cording. operator, he dials another special codeconsisting of the digits 1 1 0. In this case, the repeaterand central oilicetrunlr are released, an dithe selector S 3.set in motion to test and seize the first idle trunlrextendi-ng to thetoll .recordingposition.

ThefinderF, selectors 5%, S6, z, S8 and connectors-C and C1 may be of any well-known type such asthe two-motion StrowgersWitch having vertical and rotary by-step type.

A detailed description Wlll'gIlOW "be given, and "11] will first be assumed forthis purpose that thesubscriber of line'100 a't-the branch office wishesto extend a connection to alocal subscriber's line such as'the line 221. The

initiation of theca'll :causes'the operation of -finderswitch E, which sets itsbrushes102,

103, and 104 on the terminals'of the calling switch, groundpotential isapplied through the brush 102 to the sleeve conductor 133, which extends through-the inner leftnornial contacts of relays 115, 111,112, 1 13,'conductor 134, winding of relay 106 tobattery. Relay 106 operates and extends the'tip and ring During the operation of the finder conductors of thesubscrib'ers line to the armatures of relay i110. Relay 106 also initiates'the hunting operation of the rotarv selectorswit'ch S'-1. The .operatin g circuit 01' the switch"S1 maybe traced irom'battery through the winding and contact of steppingmagnet 200, conductor 226, inner lower contact of relay 106, conductor 135', inner 'upper'back contact of relay 110, conductor 1536 to thetest brush 20.1 of the switch'S l. if the switch S 1 is standing on a busy trunk. ground potential on the brush 201 causes the magnet 200 to operate and step, the brushes to the next position. The magnet interrupts its own circuit, and thestepping continues until an idle trunk 127 is reached. During the hunting 'movement'ofthe switch S1,

another circuit also exists by way of conductor 226 through the windingof relavlld rninals" are. encountered. When the Ifirst idle terminal is reached, the shunt-.is-renioved and relay 110' operates, opening; the'stepping cirthe conductors ofth'e callingline over the branch 125, 126 through-brushes208 1511161 205 to the trunk 127. Relay110 being of high .resist- .of relay 302 and the lower winding of relay 300'to ground. Thus, the impulse relay 300 is included in series with the conductors of the calling subscribers line 100. Relay 300 operates and closes an obvious circuit for the slow release relay 303. Relay 303 at its lowermost contact applies ground potential to the holding conductor 322. This ground poten tial is returned over conductor 323 tl'irough the test brush 201. conductor 136, inner upper front contact of relay'110 to the conductor 133 and serves to hold the finder switch F. Vithrelays 300 and 303 operated, bridge is close'dacrossthe conductors oi trunk 321 extending to the selector switch S-6 in the distant central oifice. This bridge may be traced'irom the conductor 324 through the upper contact of-relay 303, upper back con- 'tact of relay 304. upper windin of relay 301,

through the lower winding of relay 301 to ground at the contact of relav 303. Relay 3011 issn electro-polarized relay which will not operate due to its lower winding alone and will only operate when its lower winding is energized and currentflows through its 'upper'wiuding in the proper direction. The

closure of the trunk prepares the selector switch S 6 for the receipt of the first series of impulses. Relay 306 when operated places ground potential on the chain circuit 326 which erte'ndsthrough thecontacts of similar relays related to other repeaters to the all.-

trunks-busy register device 319. The direction oi. current flow from the selector switch frames 317 and 318 associated with the repeater may be wired in any desired manner to enable the use of different digits to identity the destination of the call. As shown in the drawings, it is assumed that local calls areidentified by a code consisting of the 7 digits 6 3.. Then the subscriber manipulates his impulse transmitter 101 to send the first series ofsirr impulses, relay 300 releases on the first opening of the line andcompletesa circuit from ground through its back contact, armature and front contact of relay 303- and thence in parallel through the winding of relay 304 to batteryand over conductor 327, lower con- 1 tact of relay .308,conductor 328, through the winding of the stepping magnet 314 of the register switch. Relay 304 is slow to release and retains its armatures attracted during the impulse series. The magnet 314 energizes to cause the advance of wipers 315 and 316 to their first position contacts. Relay 304 revises the trunk loop circuit extending to the central oflice so that it may now be traced from conductor 324 through the upper contact of relay 303, upper front contact of relay 304, upper contact of relay 305, lower armature and contact of relay 300 to the opposite'conductor325. This excludes the re lays 301 and 306 to improve the pulsing conditions. Relay 300 in opening its lower contact when the first impulse is transmitted, opens the bridge across the trunk to cause the repeating of the impulse over the trunk 321 to the selector switch S6. In like manner,

thereinaining impulses of the first series cause the stepping of the register switch and are also repeated over the trunk to set the selector S6.

lVhen the register switch takes its first step, brush 315 engages the contacts connected to conductor 329, and a circuit is completed from the grounded conductor 322, lower back contact of relay 307, conductor 330, brush 315, conductor 329, brush 202, uppermost front contact of relay 110 through the upper winding of relay 108 to battery. Relay 108 operates and closes an obvious circuit for slow-release relay 109, which energizes and connects its grounded'armature to the holding conductor 133. Relay 108 also operates the relay 116 on a circuit traceable frombattery through the winding and contact of magnet 200, conductor 226, winding of relay 116, lower contact of relay 108, conductor 139 through the outer left contacts of relays 113, 112 and 111 to the grounded conductor 133. Due to the high resistance of relay 116, the stepping n'iagnet 200 does not operate in series therewith. The relay 116 initiates the hunting operation of the selector S2 to preselect an idle trunk extending to a local selector. Stepping magnet 207 of the switch S-2 is energized in a circuit from battery through its winding and contact, conductor 140, left contact of relay 116, inner upper back contact of relay 107, conductor 141 to the testing brush 210. The switch continues to operate until an idle ungrounded terminal is reached, at which time the magnet 207 fails to receive energizing current and the switch comes to rest. I

At the end of the first series of impulses, the register switch comes to rest with its brushes 315 and 316 on the No. 6 contacts. and slow-release relay 304 releases after an interval. Relay 304 completes a circuit from the grounded conductor 322, lower back contact of said relay, inner lower contact of relay 307, conductor 331, brush 316, thence to conductor 332, next to the inner right "armatureand back contact of relay 312,:in-

sner right rrarmature and back contact and right-hand winding of relay-311to battery.

Relay 311 is so adjusted'that its'righ twinding when energized is sufiicient to :close its inner left'front contact andits outer right :front contact. but does not shift the remainingcontacts until the left winding is energized. The same is true of relays-312 and 313. Relay 311 at its inner left contact closes a circuitfrom battery through both its windings and said contact to the grounded conductor v323. Theleft Winding of the relay, however, is shunted by the presence of. ground on conductor 332 and,.therefore, is not efiective at this time. Relay 311 at its outer right contactrclosesla circuit for energizing'the relay 307. Thiscircuit may be traced from ground 1 through the outer right front contacts and 'next to the outer right back contacts of relay i311, conductor 333, winding of relay 307 to battery. vRelay 307 at its inner upper front contact closes a'locking circuit for itself extending throughthe lower ofhnormal contacts' 309 of-the register switch to ground atthe front contact of' relay 303. At its inner lower contact, relay 307 opens the original. energizing circuit of relay 311, and

'theshunt now being removed, said relay energizes in'the circuit'including both its windingsl Relay 311 thereupon shifts its remaincontacts removing ground potential from the conductor 333. Relay 307 at its uppermost: contact. closes an obvious circuit for the release magnet 310 which energizes and restorestoxnormal the brushes315 and Y316 "of the register switch; 'As the switch returns to normal, the contacts309 reopen, and

clay 307releases, in turn releasing the magnet-310. Due to the fact that the brush315 7 has returned to normal, ground potentialis Esecondselector switch S7.

removed from conductor 329, permitting'rela-y: 108 to release,:-'whic'h in turn releases re- The subscriber now dials the second code digit consisting of three impulses. The register switch responds to these nnpulses andadvancesits brushes to the third position. Relay 304- reoperates, and impulses arerepeated to the central .othce to set the p The relay 108 is're'operated causing the-reoperation of relay 116. Attheend of'the series, the relay 304: releases, and a circuit is'compi'eted from the grounded conductor 322, lower back contact of relay 304,-inner lower contactof relay307,

conductor 331, brush "3131 11 position conduc'tor. 334 through the frame 317, conductor iductorgl33'. 'Relay 1:15 opens the circuit of but its high resistance prevents the operation of the stepping magnet. With relay 106 released and relay 107 operated, the subscribers line is extended through the rotary selector 'S2 tothe first-local selector 8-4. This circuit maybetraced from the finder brush 103 over the upper back contact of relay 105, upperback contact of relay 106, upper frontcontact of relay 107, conductor 128,-brush 209 to conductor 228. V The other side of the linemaybetraced from the finder brush l0 1'through the lower back contacts of relays 105 and 106, lowerfront contact of relay 107, conductor 129, brush 208 to the conductor 229. The conductors'228 and 229 are connectedt-o batteryand groundat the selector switch 8-4 in the usual manner. During the switching of-the subscribers line from the repeater to the selector switch S-4, ground potential is maintained on the conductor 133 by reason of the slow-release character of relays 303 and 109 'Beforethese relays release to remove ground potential from said'conductor, a substitute potential is returned to this conductor from the selector switch S e over the sleeve circuit 230, brush 210, conductor 141, inner'upper armature and front contact of relay 107' to conductor, 133. vThe release of relay 106 opens the circuit-10f. relay 110, and this latter relay releases disconnecting the upper =windingofrelay 108 from'thebrush 202. Relay 109 releases after aninterval following the deenergization of relay 108. Relay 108 upon releasing causes the. release of relay 116.

The disconnection of the V subscribers line from the repeater R causes the release of relay 300, which is followed after. an interval by the release of relay 303. iRelay 303 removes ground potential fronrconductor 322, releasing the relay 311. I Relay303iclosesa circuit from ground through its lower back contact, off-normal contacts 309, winding of relay 307 to battery. Relay 307 energized closes a circuit for release magnet 310, (which restores the .registeris'witch to =nomal. The reg ster switch in its normal positionvopens the .springs309 and permits relay 307 to release. i

The calling subscriber proceeds to transmit the remaining series of impulses to cause the setting of selector switch 5% and connector switch'G'to complete the connection to the called line 221. When the conversation is completed, the

subscribers replace their receivers upon the switchhooks, and ground potential is removed from conduct-M230. This permits relay 115 to release, in turn releasing the relay 107. The-removal of ground potential from conductor 133 also brings about the releaseof the finder switch F.

Assume next that the subscriber ofline 100 wishes to establish a connection with a centralptlice'iinesuch as the subscribers line 320. The initiation of the call causes the operation of the finder switch and the extension of the line over the rotary switch Sl to therepeater R as already fully explained.

Since the call is forthe central oifice, the code portion of the designation maybe made up of any two digits other th the combinations 6 3, 0, and 1 1 0. It will be noted from an inspection of Fig. 3 that anycode combina tion other than the ones reserved for local calls and operators calls will result in the operation ofthe relay 308 either at the end ofthe first series of-impulses or at the end of the second series. Assume for instance that the first two digits are 6 and 2. The first digit 6 causes the register switch to take up its corresponding position. During the set- 35 ting of the register switch, conductor 329 is grounded, resulting in the operation of relays 108, 109 and 116 and also the operatlon of the rotary switch S 2. \Vhen the register switch has been fully positioned on its No.

, 6 terminals and relay 30 1 releases, relay 311 operates as above described. Relay 311 closes acircuit for relay 307, which operates and closes a circuit for magnet 310 to bring about the release of the register switch. The next idigit 2 causes the positioning of the switch on its No. 2 terminals, and upon the release of-relay 30 1, a circuit is completed from grounded conductor 322,, lower contact of relay 304, innerlower contact of relay 307,

conductor 331, brush 316 in position 2, conductor 337 through the frame 317, conductor 333, normal contact and winding of relay 308 to battery. Relay 308 operates and locks through its inner upper front contact to ground through the inner lower contact of relay 303. Relay 308 completes a circuit from battery through the winding of relay 307, uppermost contact of relay 308, conductor 338, thence as previously traced tothe grounded conductor 322. Relay 307 energizes in this circuit and locks through its inner upper front contact through the lower oifnormal contacts 309 to ground at the front contact of relay303. Relay 307 is so adjusted that closes its inner upper contact before it opens its inner lower contact, thus insuring the, locking of the relay before its operating circuit is opened. Relay 307 energizes the release magnet 310, and the register switch is restored to its normal ppsition.

Since ground potential is not applied in this case to the conductor 336, relay 115 does not-operate: Relays 108, 109, and 116 release as above explained. The subscriber continues to transmit the remaining di its,

current is reversed over the trunk 321 causing the operation of the electro-polarized relay 301. Relay 301 operates the relay 302, which reverses thedirection of current flowing over the subscribers line. This may serve to bring about the operation of a message register. Relay 302 modifies the circuit extending to the central office so that it now leads from the conductor 324 through the upper contact of relay 303, upper contact of relay 301, upper winding of the latter relay, upper front contact of relay 302, uppermost windin of relay 306, back contact of relay 305, lower contact of relay 300 to the conductor 325. This includes the additional resistance of the relay 306 in the talking cir cuit to improve the transmission characteristics of the line.

When conversation has been completed, the calling subscriber replaces his receiver causing the release of relays 300 and 303. Relay 303 removes ground potential from the holding conductor permitting the release of the energized relays in Fig. 1 and also the restoration of the finder switch F.

Assume next that the subscriber of line 100 wishes to call the special service operator. On initiating the call, his line is extended throughthe rotary switch S-1 to the repeater R in the manner above described. To call the operator the subscriber dials the digit, 0. This causes the setting of the register switch on its tenth position contacts. As the brush 315 leaves the ninth position contact, it removes ground potential from conductor 329 permitting the. release of relays 108 and 116.- The register switch in position 10 closes a circuit for operating relay 305. This circuit may be traced from battery through the winding of said relay, conductor 339, normal contacts of relay 312, normal contacts of relay 311, conductor 340, brush 315 to ground overcon'ductor 330 as hereinbefore explained. Relay 305 completes a circuit from ground through its lower contact, conductor 3 11, brush 204, conductor 231, through the lower inner front contact of relay 110, right'back contact of relay 116, right winding of relay 112, left contact of relay 120, inner right contact of relay 119, outer right contact of relay 117 resistance 118 to battery. Relay 112 operates and looks through its left winding and contact, left contact of relay 111 to the grounded conductor 133.

It may be noted at this point that relays 117, 119, 120, 121, 122, and 123 are common to a number of trunk circuits such as the one shown in Fig. 1. The relay 112, which is individual to the particular trunk circuit shown, and which receives its energizing potential from battery through the common resistance 118, is so adjustedthatit will not operate. inparallelwith the relay 11 1 of-any other siinilarcircuit. Likewise, the relay 114: is adj usted'so that itwill not operate in parallel'withanother relay 112. Thepurpose of this-adjustment is to prevent a switch S3 frorn'startingfto hunt for one type of op-- erators trunkappearingin its bank before another switch has completed ltS- huntlng for I. atrunk of the othertype. The relay 112, for

instance, indicates that the call is for a special operators trunk whereas the relay. lldindi cates, that the-call isfor. a recording, trunk.-

Bothzof these trunksappear in the multiples o1 selector switches; S,-3 and, therefore, it is necessary :to prevent a-second'switch hunting for one kind of'trunk while'a first switch is still in the act'of huntingfor atrunkof the otherkind.

Relay 112 when operated, as above de-- scribed closes a circuit-from battery through through tl1616f1330011t2t0h0f relay 117,.righ

the winding or relay 117, outerright contact of relay112,.conductor142to ground at the back contact ofrelay-105. Relay 117 at its inner. contactreinoves battery potential from the; windings of all relays 11 1 in the group.

Should a call be made-for. a toll; recording trunk before the operators trunk is selected, relay 111 isoperated ina-circuitfronibattery winding of relay 111,,0uter rightfront contact of: relay 116 (thelatter relay being operated-in thiscase) to ground over conductor 231; Relay 111 f operates and connects the busytone circuit 124; throughits right cons tact, left: contact of relay 115through the lower winding of relay 108 thence over'the SLlbSCI'lbGI'IS loop; and returning to ground ing the operatingtimeof'selector. S 3.

Relay '12ialsolinitratess the movement of therotary switch S'-3. The'operating circuitmay be. traced from battery through the winding and-contact of magnet 211, inner right contacts of relay- 112, conductor 1 13,

inner: upper; back contact, of relay 1055, conductor-144', to .the test brush2-14. A parallel circuit extends over theinner-right contacts of relay. 112'through=the winding of relay 105.to:ground.- Relay.;105' is shunted, however, so long; as thebrush 214 encounters grounded [contacts Since the switch S3 is seeking an: idle special servicetrunk, all trunks leading; to the-toll E recording position shouldappear artificially busy inztheyswitch.

The recording trunk 223,-.forinstance, is pro videdwith an. individual .relay 220 which .connectsground potential through its back contact to the test terminalin: the. switch S-3. If the trunk is actually busy, the relay 220 will be operated and the busy potential is then extended through the-front'contact of therelay to the switch contact. The same is true of the neXtrecording trunk 225, which is maintainedin a nonselectable condition by the relay 219. The special service trunks such as the trunks 222 and22 1 areprovided' with individual relays-217, 218' and 215, 216 respectively. If the first'trunk 222. is busy, relay: 218' will be operated and the busy ground potential is then. extended through the upper contact of relay 218'to the test terminal in the switchS-Zl. The same is true ofthe trunk 224-5 Assume that the trunk 224: is idle. When, therefore, the test brush 21 1 reaches its third contact, no ground potential. is found sincerelay' 216 'is released, and relay 105 immediately operates in series withthe-rnagnet 211. Due-to'the resistance of relay 105, the magnet cannot operate.; accordingly the switch comes to rest.

As soon as the selector S3 finds the idle trunk 22 1, ground is returned over the sleeve conductor to operate relay 216, which further. extends the ground potential overconductor through the inner upper front contact of: relay 105, which is-now operated, to the holding, conductor 133'. Relay 105 in operating. releases relays 108 and 109;and' extends the. conductors of the subscribers linethrougln to the brushes 212 and 213 of the rotory switch. S-3Iand thence over, the trunk 224' tothe; operatorsposition. r 7

1V hen the call has beencompleted, ground is removed from the holding conductor 133,-. and relays 105, 112, and 117 are released.

Assume next-that the subscriber of line 100 wishes to extend a connection to atoll position reached over; one ofthe trunks 223,225, etc. In this case he dials the special code 11: 0. On the completion ofthe first digit 1', the

grounded'conductor 331 is extended over the brush 316to conductor 342, back contact of relay 311, inner right'back contact and'right; winding of relay 313 into the battery. Relay 313 partially operates and in so doing completes a circuit. from ground'through its right contacts over conductor 33-3 to operate; the relay 307. Relay 307 brings about the release of the register switch, andthereupon: the relay 313 fully operates and locks to con ductor 323. On the completionofthe next digit 1, the grounded, conductor 331 is ex tendedover conductor 342 throughtheback contacts of relay311, inner'right front contact of relay, 313, inner right contact and right winding of-relay 312 tob'attery. Re

lay 312 partially operates and operates the relay 307, which restores the register.

switch to normal. Thereupon. the relay 312 fully operates and locks to the con places ground potential on conductor 341.

With the switch in position 10. the grounded conductor 330 is also extended over conductor 340 to theback contact of relay 311 front contact of relay 312, conductor 329. The grounded conductor 329 causes the operation of relay 108 as above explained. The grounded conductor 341 extends through the brush 204, conductor-231, contact of relay 110 the right-hand armature and front contact of relay 116,winding of'relay 114 through the common resistance 118 to battery. Relay 114 operates relay 119in an obvious circuit. Relay 114 also operates all relays 215, 217, etc., individual to the special service trunks in order to render these trunks artificially busy so they will not be seized by the switch. S-3. At the same time, relays 219, 220, etc. are operated toremove the artificially busy condition normally existing on the toll recording trunks to-permit an idle one of these to be selected. The circuit may be traced from ground through the inner lower contact of relay 105, conductor 142, right contact of relay 114, conductor 145, thence in 3 parallel through the windings of relays 215,

217, 219, 220, etc. to battery. It the special service trunk 224 is actually busy relay 216 is operated to extend the busy condition through its inner upper contact to thesleeve conductor 232. If the trunk is idle, the operation of relay 215 renders it non-selectable by means of a circuit from ground through the lower contact of relay 216, contact of relay 215 to the test conductor 232. The same is true of all other trunks leading to the special operators position. If a recording trunk such as the trunk 223 is busy, its individual relay 220 is already operated to extend the busy condition through its front contactto the test conductor 233. If, however, the trunk is idle the relay 220 is operated over conductor 145, as explained, to remove the artificial busy condition.

Relay 119 at its inner right contact removes battery potential from all relays 112 in the group. At its left contact, it applies battery potential to the middle winding of relay 111 so that if a call is subsequently made for a special service trunk before the recording trunk has been selected relay 111 will operate in a manner similar to that hereinbefore described to connect the busy tone conductor 124 to the calling subscribers line. Relay 114 operates relay 113 which is slow to attract its armatures so as not to start the hunting of switch S3 until the trunk relays have been fully operated. Relay 113 looks through its left contact and the contacts of relays-112 and 111 to the grounded conductor 133. Relay 113 at its right contacts closes substitute circuits for relay 119 and also for the other relays energized over conductor 145 by the relay 114. Relay 113 initiates the operation of the switch S3 by means of a circuit from battery through the winding and contact of magnet 211 through the inner right contact of relay 113 and thence over conductor 143 as previously traced to the test brush 214. When an idle toll recording trunk has been found, relay 105 operates and causes the switch to cease its hunting operation. Relay 105 also extends the subscribers line through to the toll recording trunk selected. The central ofiice trunk is released in the manner already fully described.

l/Vhen conversation has been completed, ground potential on the holding conductor 144 is removed in turn removing potential from the conductor 133. This permits the release of all energized relays and the restoration of the equipment to normal.

hould all of the special operators trunks become busy, relays 216, 218, etc. are all energized and ground potential is removed from conductor 146. This permits the release of the normally energized relay 122. Relay 122 operates relay 120, which opens the common circuit to prevent the operation of any one of the relays 112. Relay 120 at its right contact applies battery potential to the middle windings of all relays 111 so that if an operators call is attempted the busy tone is sent to the calling subscribers line. In like manner if all of the toll recording trunks are busy, ground potential is removed from conductor 147 to permit the release of relay 123, which in turn operates relay 121. Relay 121 opens the common lead to prevent the operation of any of the relays 114 and applies battery potential to the right windings of all relays 111 so that if a toll recording call is initiated the busy tone is transmitted to the calling subscribers line.

What is claimed is:

1. In a telephone system, a line, a circuit having three branches, automatic switches, each of said branches terminating in a separate one said switches, means for connecting the line to said circuit, trunk lines appearing in each of said switches, selector switches to which said trunks extend, means for operating one of said automatic switches to extend said line over one of said trunks to the corresponding selector, means for send ing impulses over the extended connection to operate said selector switch, and means depending on the number of impulses sent for releasing the extended connection and for extending the line over one of the trunks appearing in another of said automatic switches.

2. In? aiteleplione system, ailine, attrunk having.v a pluralityof: branches, automatic S\V*Itl18S,- each of said branches-terminating:

ina. separate one of saidswitches, means for extending the line to saidltrunlgitrunk circuits appearing; ineach of. said; switches, means-for operating'one of said automatic switches to extend the line over one of said trunk circuits, means for sending, over the extended connection impulses representing a;des1red designation, and means depending;

uponthe nature of said designation for releasingrthe extended connection and forsalectively extending the line over one of'a number of said other automatic switches.

3. The combination in a telephone system of; a- SHbSCIlbGI SllHQa trunk terminating in the. brushes of a plurality of automatic switches, means for extending the-line to said trunk, trunk circuits appearing in'the termi+ nalsof said automatic switches, means responsive to the extension of the subscribers line to said first mentioned trunk for operating one; of saidautomatic switches to further. extendthe connection to the trunkcir cuits appearing, therein, means for transmitting; designationimpulses over the extended connection, means responsi-vejto the transmissionof saidimpulses for operating. a second oneofsaid automatic switchesto seize an idle one/of the trunk circuits appearing. in the terminals thereof, and means dependent upon r whether such switch is to be released and the through a third one switches.

the wanted designation for determinating whether theconnect on is to continue its progress through the first selector switch or connectionfrom the subsoriber7s line extended through said second automatlc switch or or" said automatic 4; The combination in a telephone system of av subscribers line, three separate-trunk hunting. automatic switches, a connecting-circuitiappearingin the brushes of each of said automatic switches, means-for extending the subscribers line to said connecting circuit,

trunks appearing, in the terminal banks oi" said automatic switches,.means for. operatmg one of sa1d automatic switches to extend the subscribers line over one of said trunks, means for transmitting designatmn impulsesover the extended connection, means responsive to the transmission of sald impulses tor mltiatmg the movement of a second one of said.automaticswitches to preselect an-idle trunk, and means responsive to said designation impulses and dependent uponthe nature of the designation for releasing, the co-nnec-V tionextended over said first automatic switch, foroperating the third one of said automatic switches to select an idletrunk and for extending, the subscribers line through said third automatic switch to the selected idle trunk.

5. In a telephone system, a branchoflice;

havin g a plurality 1 of: automatic trunk hunt ing switches, aconnecting; circuit appearing inthebrushes oteach otisaid s ches, a su scribersline, means for. extend scriberFsline to-saidconnecting circuit, a cen tral otlicehaving. se-lectora switches therein,

trunks appearingin thebanks o'f one'of said SLZCllGCEZl selectorswitches or through a third one ot-saidautomatie s 'itches.

ln a'telep'hone system, asu'oscribers-line a: plurality of automatic trunk hunting swit. hes, a@c-onnecting circuit terminating in cachet said switches, anon-numericalswitch for" GXtBHChfig" the subscriberslineto said connecting circuit; agroup ot trunks appearmg in one of saldlautomatic switches, a sccond group of trunks appearingin a second cne of said automatic switches, athird-andafourth group oftrunks'appearing in the third one of said automatic switches, means for xtending the subscribefls line over the first one of said automatic switches in response to the initiation of acall, means for sending desig nation impulses over the extended connection, means responsive-to saidimpulses and'dependent: on the designation for releasingthe c entraloliice, local selectorw extended connection-and for routing the callingj subsc-ribers line either through said secondior said thirdautomatic switches, and means alsodepeudent on the wanted designation for determining whether the subscribers line is tobe; extended over trunk in the third grouper over a: trunk in the fourth group appearing in said third automatic switch. I p

7. In a telephone system, a-line, a trunk, a selector switch in which said trunk terminates, an automatic switch for conn ctingthe line to said trunk, means-for sending over the connection impulses designating a called station, airepeater in saidtrunk for repeating said impulses over the trnnkto operate said 0 I said repeater Ior recordlnc' a certain portion of selectors, itch, a register'associated with said designatingsimpulses, second automatic switch,assecond'selector switch, a trunk ac cessible to said second automatic switch and extending, to said second selector switch, and means controlled by the register for releasing the connection extended to the first selector switchand for causingimpulsessubsequently therein, means for sending impulses to said trunk, registering means associated with said trunk and operated in accordance with the nature of said impulses for causing the release of the extended connectionover said first mentioned automatic switch, and means controlled by said registering means for routing the calling subscribers line over said connectci-rcuit through either of a number of said other automatic switches to an idle trunk appearing therein.

9, In a telephone system, a subscribers line, a plurality of automatic trunk hunting switches, a connecting circuit appearing in the brushes of each of said switches, means for connecting the subscribers line to said connecting circuit, trunks appearing in the terminals of said automatic switches, means responsive to a call on the subscribers line for extending a connection over said connecting circuit and through a first one of said automatic switch to an idle trunk appearing therein, registering means associated with said last mentioned trunk, means for sending impulses to said trunk to cause the operation of said registering means, means controlled by said registering means dependent upon the nature of the impulses transmitted for releasing the connection extended through said automatic switch and for automatically connecting the subscribers line over the connecting circuit through a second one of said automatic switches to an idle trunk appearing therein, and means also controlled by said registering means in accordance with the nature of the impulses transmitted for extending the subscribers line over said connecting circuit through third one of said automatic switches to an idle trunk appearing therein.

10. The combination in a telephone system of a subscribers line, a plurality of automatic trunk hunting switches, trunks appearing in said switches, a connecting circuit appearing in the movable terminals of each of said switches, means for connecting the subscribers line to said circuit, registers associated with the trunks appearing in a first one of said automatic switches, means responsive to a call on said line for extending the same over the said first automatic switch to an idle trunk, means for sending a number of series of impulses over the extended connection, means responsive to a portion of said impulses for operating the corresponding register, means controlled by said register for determining whether the connection is to continue over said first automatic switch and the associated trunk ap earing therein or whether such connection 1.; to be released and the calling line extended. over said connecting circuit to another of said automatic switches, and means also controlled by said register for determining the particular one of said other automatic switches over which the connection is to be further extended.

11. In a telephone system, a selector switch having a row of contacts and brushes coacting therewith, two groups of trunks appearing in said contacts, relays, one for each of said trunks, the relays of one group serving when released to maintain the corresponding trunks artificially busy, the relays of the other group serving when operated to maintain the corresponding trunks artificially busy, and means for selectively operating said groups of relays.

12. In a telephone system, a selector switch having a row of contacts and brushes coacting therewith, two groups of trunks, the trunks of said groups appearing promiscuously in said contacts, relays, one for each of saidtrunlrs, means for selectively operating a portion of said relays, means controlled by the operated relays and by the unoperated relays for rendering one of said groups of trunks artificially busy, and means for selecting a trunk in the other of said groups.

13. In a telephone system, a selector switch having a single row of contacts and brushes coacting therewith, two separate groups of trunks appearing in said contacts, relays, one for each of said trunks, the relays of one group serving when released to main tain the corresponding trunks artificially busy, the relays ofthe other group serving when operated to maintain the correspond ing trunks artificially busy, and selective means for operating said relays to shift the artificial busy condition from one group or" trunks to the other.

14. In a telephone system, a selector switch having a single row of contacts and brushes coacting therewith, two separate groups of trunks appearing in said contacts, relays, one for each of said trunks, the relays of one group serving when released to maintain the corresponding trunks artificially busy, the release of the other group serving when operated to maintain the correspondim trunks artificially busy, andselective means 101' operating said relays to shift the artificial busy.

conditions from one group or trunks to the other.

15. In a telephone system, a selector having a row of contacts and brushes coacting therewith, two groups of trunks appearing in said contacts, relays, one for each of said trunks, the relays of one group serving when released-to maintain an artificial busy condition on said trunks and when operated to maintain an actual busy condition on said trunks, and selective means for operating 'said relays to shift the artificial husy condition from one group of trunks to the other.

16; In combination, aselector switch having a row of contacts and brushes coacting therewith, two groups of circuits appearing 'promiscuously in said contacts, relays, one

for each of said circuits, certain of said re lays serving when deenergized to render the corresponding circuits non-selectable, other of said relays serving when energized to render the corresponding circuits non-selectable and selective means for operatingsaid relays to change the-non-selectable condition from certain of said circuits to other of said circuits.

17.- In a telephone system, a line, a'circuit-having a plurality of branches,-'automatic SWltCh6S,-'6'3Cl1 of said branches terininating in a separate one-of-saidswitches, means for-extending the lineto said circuit,

trunks appearing in eachof said switches,

means responsive on the connection of said circuit to said line for operating one otsaid switches toextend the line over a trunkappearing in said switch,- means for sending over th-eextended connection a series=of impulses representing a desired designation,

means responsive to the first seriesof impulses for actuating another-of said switches" to select an idle trunkappe'aringin said other switch, and means responsive tov a second series of impulses for releasing the'extended connection and for extending the line through said other switch to the idletrunk selected thereby.

In witness whereof, I hereunto subscribe myname this 21st day of March, 1930.

' i 'HENRY HOVLAND. 

